This Phase I SBIR grant application enables the development of Pulsed Ultrafiltration (PUF) by Lab Connections, Inc. with the support of the inventors - Profs. Duane Venton and Charles Woodbury, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago. PUF is a rapid technique for the quantitative measurement of intermolecular affinity, capable of generating data on the strength, location, kinetics and thermodynamics of large/small molecule binding. It uses no intrusive molecular labeling, allows molecules to interact in free solution and is optimized for large/small molecular interactions. A pulse of ligand is passed through a cell containing receptor molecules confined by an ultrafiltration membrane. Any binding alters the elution profile of the ligand from which the binding density as a function of free ligand concentration is derived. A prototype PUF cell developed at UIC will be miniaturized to improve response and sensitivity. The cell will be integrated with a standard HPLC autosampler, pump, UV detector and Pentium PC. A Microsoft Windows based operator interface will be designed to control the instrument, analyze the data and present the results. System performance will be established by comparison of the data obtained on several, well characterized molecules with conventional methodologies. PROPOSED COMMERCIAL APPLICATIONS: Drug discovery by library screening is increasing exponentially, as are the number of interesting drug candidates (hits) isolated. A rapid method for ranking the hits by activity is urgently required. There are 3000 - 5000 laboratories world-wide involved in the drug discovery process. The potential annual market for PUF is estimated to be $75m today, growing to $250m in five years.